Method for protecting a welded joint between pipes having an interior coating

ABSTRACT

In the proposed method, a protective sleeve is plastically deformed to dimensions enabling the shape of the sleeve to correspond to the shape of the interior surface of the pipes to be joined in the joint region. The deformed sleeve is installed inside the pipes to be joined such that an annular cavity is formed between the sleeve and the region of the welded joint together with the adjacent portions of the pipes protected by a coating. The ends of the pipes are joined by welding and the annular cavity is hermetically sealed at the ends of the sleeve. Once sealed, the cavity is evacuated and, via working apertures in one or both of the pipes to be joined, the annular cavity is filled with a liquid sealing material, which is then polymerized. During installation of the protective sleeve, a steel cushioning ring can additionally be positioned between the sleeve and the welded joint, wherein the outside surface of the cushioning ring contacts with the surface of the welded joint and the inside surface of the cushioning ring is provided with projections which contact with the outside surface of the sleeve. As the joint is welded, the ends of the pipes are welded to the steel cushioning ring. The technical result is more reliable and durable corrosion protection of a welded pipe joint.

FIELD OF TECHNOLOGY

The invention refers to the construction of pipelines and can be usedfor purposes of anti-corrosion protection of inner welded joints ofpipes with an inside protective coating.

STATE OF THE ART

A state-of-the-art method for inside anti-corrosion protection of weldedjoints of pipes with an inside protective coating is known in theliterature which comprises a preliminary cleaning of the welded-jointzone and adjacent areas of the inside protective coating, application ofan adhesive compound resistant to corrosive environment onto a bandage,formation of a protective bandage belt after making a welded joint bymeans of introduction of the bandage into the inner space of the pipewith subsequent pressing of the bandage to the inner surface of thewelded-joint zone, and solidification of the adhesive compound in theprocess of heating. As the bandage, a sealing fiber-reinforced filmliner is used. It is made of corrosion-resistant materials and comprisesa film impermeable to corrosive environments and doubled on bothsurfaces with an adhesively bonded layer made of a fibrous materialimpregnated in a vacuum chamber with solvent-free liquid binding agentwhose chemical formula is very similar to that of the pipe coatingmaterial and capable of forming stable bonding to the material of theinside protective coating of the pipes. The protective bandage belt isformed by means of pressing the bandage to the inner surface of thewelded ends of the pipes with partial overlapping of the insideprotective coating of the pipes (RU 2328651 C1, published 10.07.2008[1]). The method has the following drawbacks:

1) In the process of insulation of such welded joint, which comprisesthe inflation of the elastic element of the expandable device withcompressed air, there arises an elevated risk of a puncture of theairtight polyethylene/polypropylene bandage film by burrs and/or iciclesthat appear at the joint root in the process of welding. Therefore, oneneeds to implement special, rather laborious measures aimed atprevention or removal of such burrs and/or icicles in the welded jointzone.

2) It is not feasible to insulate hardly accessible and inaccessibleinner welded joints, for example, in the course of making large-sizedpipe strings, offsets, bends, joints in cases of repairing localpipeline areas etc.

3) The time of pipeline construction grows considerably due to theimpossibility of performing assembly & welding operations before thefull completion of insulation and visual control of the quality of thelast welded joint.

4) The visual quality control for bandage application does not allowcontrolling the airtightness of welded-joint insulation, detectingpunctures of the sealing film by burrs or icicles, or othermicro-defects of anti-corrosion protection in the welded-joint zone.

A Butler (US) patented method for expanded-end connection of pipes withan inside anti-corrosion epoxy coating is known in the literature. Tomake an expanded-end connection, ends of the pipes are subjected toplastic deformation prior to application of an anti-corrosion epoxycoating. At one end of the pipe, a flaring is formed by means of thecold-expansion method with the help of a punch. The other end of thepipe is subjected to plastic squeezing using a die to achieve a shapethat allows a sufficiently firm contact with the inner surface of theflaring in the case of coercive matching with a required effort. Toensure the tightness of the expanded-end connection, a sealant agent isapplied onto the matched surfaces of the pipe ends (V. N. Protasov.Analysis of deficiencies in current technologies for connection of pipeswith an inside epoxy coating when constructing oilfield pipelines, andadvantages of welded joints with an inside anti-corrosion insulation ofthe weld with a banding. Territorii Neftegaz Journal. March 2009, p.21-22, FIG. 2 [2]). This method has the following deficiencies:

1) The need of extra process operations (prior to application of theprotective coating) using some specialized equipment to provide therequired profiling of the end portions of each pipe, which increasessignificantly the cost of the pipes with an inside coating in the caseof the given method for their connection.

2) The need to employ expensive special mechanized devices for coerciveassembling of the expanded-end connection in field conditions.

3) At the majority of enterprises involved in insulation of oil and gaspipelines with polymer coatings, including pipe plants, an insidecoating is applied onto the pipe with even ends, to which the Butlermethod for expanded-end pipe connection is not applicable.

4) There are also no data on conservation of cold brittleness of thewelded joint after the formation of the expanded end by means of plasticdeformation on welded pipes, which is of particular significance forconstruction of oil and gas pipelines in the Far North.

The closest method to the proposed one is that of the Tuboscope-Vetcocompany (USA) (V. N. Protasov. Analysis of deficiencies in currenttechnologies for connection of pipes with an inside epoxy coating whenconstructing oilfield pipelines, and advantages of welded joints with aninside anti-corrosion insulation of the weld with a banding. TerritoriiNeftegaz Journal. March 2009, p. 21-22, FIG. 1 [3]). The method ofinside anti-corrosion protection of welded connection of pipes with aninside protective coating comprises placement of a steel liner coaxiallyinside the pipes to be joined, with formation of annular cavities andgaps between the outer surface of the liner and the inside surface ofthe welded pipe joint (to be insulated) with adjacent coating-protectedareas, as well as sealing-off of the annular cavity at liner ends. Asealant agent is used to seal off the gap between the outer surface ofthe protective liner and the inside pipe coating. The sealant agent isapplied onto the inside coating of the pipe ends to be attached togetherprior to placement of the protective liner. When the latter is being putinto the inside space of the pipes to be connected together, the rubberrings with an annular section placed in special grooves on the outersurface of the protective liner move the sealant agent along the axialdirection, which ensures the formation of sealing beads in front of theprotective-liner ends. In the central part of the protective liner, onits outer surface, a special groove is provided, which enables an airlayer between the liner and the inside surface of the pipes beingconnected in the area of welding, and hence prevention of heat-induceddecay of the protective coating of the liner. For the same purpose, aspacer made of a special heat-resistant cloth with low heat conductivityis placed on the surface of the protective-liner groove. To ensure thepositioning of the liner relative to the welded joint, at the center ofthe liner groove three radial thin steel petals are welded, which arepositioned between the ends of the pipes to be welded and are meant toform an organic whole with the welded joint after the welding.

The known method and connection [3] suffer from the followingshortcomings:

1) Difficulties with achieving the airtightness of the non-uniform andrather sizable gap between the protective liner and the inside surfaceof the pipe ends to be welded together, which results from a pronouncedout-of-roundness of these pipes.

2) Reduction in the pipeline's flow area at sections with the protectiveliners installed, which leads to considerable amounts of soliddepositions of substances precipitating in the course of fluid producttransportation through the pipeline, and complicates the inside cleaningof the pipeline with the help of conventional mechanical methods, e.g.pigs.

3) Poorly feasible control of airtightness of the gap between theprotective liner and the inside surface of the pipes welded together inthe process of construction of the pipeline.

4) Rather long welding operation due to necessity to observe the gapbetween the pipe ends while welding to prevent squeezing-out of thesealant agent by gases produced in the process of welding.

The closest method to the proposed one is that described by V. N.Protasov for inside liner-type anti-corrosion protection of weldedconnections of tubular formed components with an inside anti-corrosionprotection (RU 2388961 C1, published Oct. 5, 2010 [4]), according towhich: adapters with a flaring at the free end, having a transversethreaded hole in the central part are welded to ends of tubular formedcomponents to be welded together; a protective anti-corrosion coating isapplied onto the inside surface of each formed component with the weldedadapter; a sealant layer is applied onto the area of the adapter'sinside surface adjacent to the inner ledge of the adapter; a protectiveliner with sealing rings put in grooves made on the protective liner'souter surface end parts and with a one more groove made in between theabove grooves and an insulated spacer made of a heat-resistantheat-insulating cloth is placed in the inside cavity of the adapterliners to be connected together, to allow formation of an annular cavitybetween the outer surface of the heat-insulating spacer and the insidesurface of the expanded part of the adapters; the adapters of the pipesare welded together; the set of tubular formed components so made ispressurized with water to control the tightness of the inside lineranti-corrosion protection of the welded joint, with subsequent placementof threaded plugs in the threaded holes. To raise the bearing capacityof the protective liner and in cases of leaks detected, the annularcavity is filled with a sealant agent (with a high-modulus filler) viathe threaded hole of an adapter until the sealant agent appears in thethreaded hole of the other adapter.

The known method suffers from the complexity due to the necessity toweld the adapters to the pipes being joined, which results from that theprotective liner reduces the inner section of the pipes and enhances thehydraulic resistance in the welded-joint zone.

Additionally, pipes often feature a pronounced degree ofout-of-roundness and/or diameter scatter, which complicates thepressurization of a non-uniform and sizable gap between the protectiveliner and the inside surface of the pipe ends to be welded together.

SUMMARY OF THE INVENTION

The objective of the invention proposed herein is to raise thereliability and service life of anti-corrosion protection of pipelines'joint welds concurrently with streamlining the technology for insulationof such welded joints.

This objective is achieved using the method for inside anti-corrosionprotection of welded joints of pipes with an interior protectivecoating, which comprises: the placement of a protective liner coaxiallyinside the pipes to be welded together, with the formation of an annularcavity between the outer surface of the liner and the inside surface (tobe insulated) of the welding joint of the pipes with adjacentcoating-protected areas; welding of the pipe ends; sealing of theannular cavity at liner ends; filling of the annular cavity with aliquid sealant agent via at least one process hole in one or both pipeswith subsequent polymerization of the agent, in accordance with theinvention is supplemented by that, prior to the placement of theprotective liner it is plastically deformed to a size that ensuresmatching the shape of the liner to that of the inside surface of thepipes to be connected, in the area of the joint.

Also, the annular cavity is filled with the liquid sealant material bymeans of evacuating the annular cavity and subsequent feeding of saidmaterial therein, and then exposing it to atmospheric or excessivepressure.

In a particular embodiment, when the protective liner is placed, a steelannular cushion is also arranged in between the steel liner and the weldjoint, the outer surface of the cushion being in contact with the weldjoint surface and having projections on its inner surface that contactto the outer surface of the steel liner, and these projections arewelded to the steel annular cushion when welding the pipe ends together.

Additionally, one can use either the protective liner with annularprojections on the outer surface of its end parts or, when performingthe plastic deformation, make annular projections on the outer surfaceof its end parts.

In a particular embodiment, prior to placement of the steel liner, areinforcing, easily impregnable material, resistant to corrosiveenvironments, can be arranged on the outer surface of the liner inbetween the annular projections.

Besides, it is expedient to control the airtightness of the weld jointinsulation prior to and after the filling of the annular cavity with theliquid sealant material by means of evacuation and subsequent assessmentof the rate of air/gas leakage into the annular cavity.

Also, the protective liner is made of stainless steel and has a wallthickness ranging from 0.1 to 6.0 mm.

The essence of the proposed method consists in using a thin-wallprotective liner, preferably made of stainless steel with a wallthickness ranging within 0.1-6 mm, its adjustment to geometricdimensions of the ends of both pipes to be joined by means of plasticdeformation, placing the so adjusted thin-wall steel liner coaxiallyinside the pipes being connected with reduction in the volume of annularcavities and gaps due to reduction of gaps between the pipes and theouter surface of the protective liner, which is achieved throughadjustment of the protective liners to interior geometric parameters ofthe pipes being attached.

When using a thin-wall liner, on its outer surface and in the center ofthe liner, immediately in the zone of weld joint root, an additionalsteel split or continuous ring that functions as a cushion for theformation of the weld joint root is arranged. In the process of weldingthe joint, the steel annular cushion is welded to the pipes being joinedto form a monolithic joint. The steel annular cushion avertsnon-controlled spreading of a liquid metal in the annular cavity andprotects reliably, in the course of welding, the thin-wall protectiveliner from a burn-through.

On the surface of the annular cushion facing the outer surface of theprotective liner, projections can be made in the form of points,intermittent reinforcement ribs etc. A multifold reduction in thesurface of contact between the annular cushion and the protective linerleads concurrently to a multifold drop in thermal flux from the annularcushion to the protective liner, thereby averting the heatup of thesealant material to a critical point and depressurization of the sealedends of the protective liner with the insulated surface of the weldedjoint. Also, a guaranteed gap is formed between the annular cushion andthe protective liner, which, once the welded joint's annular cavitiesand gaps are filled with a liquid sealing compound, secures unhamperedfilling of the whole annular cavity with the sealant agent.

The technical effect of the method proposed consists in the following:an essential reduction in the impact of inside geometry violations, inparticular, the degree of out-of-roundness of the pipes used and a widescatter of internal diameters of the pipes, upon quality andlaboriousness of insulation of pipeline weld joints; an essentialreduction in material consumption for the protective liner owing tousing a thin-wall liner capable of undergoing plastic deformation in theprocess of pipeline construction; reduction in consumption of sealantmaterial owing to a lesser volume of the annular cavity between theprotective liner and the pipes to be joined.

LIST OF FIGURES

The essence of the invention is illustrated with the help of figuresbelow, where FIGS. 1-4 provide a schematic presentation of the stages ofthe method proposed:

FIG. 1 and FIG. 2—with supply of the sealant agent via a vacuumreservoir;

FIG. 3 and FIG. 4—with supply of the sealant agent via an extra openingin the pipe (vacuum infusion method).

In FIG. 5 and FIG. 6, a welded joint with and without a reinforcingmaterial respectively is displayed.

In FIG. 7, a thin-wall protective liner is shown in its initialcondition, prior to its adjustment to interior geometric parameters ofthe pipes to be joined.

In FIG. 8, the thin-wall protective liner is shown after its adjustmentto interior geometric parameters of the pipes to be joined.

In FIG. 9, the annular cushion with point-like projections is displayed.

FIG. 10 shows the annular cushion with projections in the form ofintermittent reinforcement ribs.

In FIG. 11, the diagram of welded-joint insulation with the help of theannular cushion is shown.

PARTICULAR EMBODIMENTS OF THE INVENTION

The welded joint of pipes with inside protective coating 3 (FIGS. 1-4)achieved by means of the method described herein comprises thin-wallstainless steel liner 5 placed coaxially inside connected pipes 1 sothat a narrow annular cavity is formed between outer surface 6 of liner5 and inside surface 7 (to be insulated) of the welded joint of thepipes, with adjacent coating-protected areas. The annular cavity isfilled, via process hole 8, with polymerized sealant material 10resistant to corrosive environments. Thin-wall liner has annularprojections 9 on the outer surface of its end parts. As an option,reinforcing material 10 (see F.5) impregnated with polymerized sealantmaterial resistant to corrosive environments can be placed in theannular cavity. Sealing-off of welded joint 2 is also ensured throughsealing-off of the annular cavity by sealant agent 4 applied as acontinuous annulus along the entire perimeter of the pipe at each end ofliner 5. In accordance with the method proposed, the thickness of thewall of protective liner 5 made of stainless steel ranges within 0.1-6mm. In the upper wall thickness range, protective liner 5 is insensitiveto a burn-through in the course of joint welding. Increasing the wallthickness to values exceeding 6 mm is inexpedient from the economicviewpoint since it does not result in improvement of functionalcharacteristics of the protective liner. On the contrary, in the case ofan excessively thick wall the deformation capacity of liner 5 worsensconsiderably, which complicates its adjustment to geometric parametersof the pipe ends. The choice of a liner 5 wall thickness somewherewithin the upper range of values is determined by the design of thewelded joint to be insulated, namely, use of an annular cushionreinforcing the heat-resistant material and special welding equipment,or special technology measures that allow welding without outflow ofmolten metal from the molten pool or a burn-through of the liner.

At wall thickness values of less than 0.1 mm, the stiffness of liner 5becomes unsatisfactory even at short diameters of the liner.Additionally, at lesser wall thickness values the protective propertiesof liner 5 reduce to a critical level. A minimal wall thickness forprotective liner 5 can be chosen on condition of using, for welded-jointsealing purposes, reinforcing heat-resistant material 10 (FIG. 5) andannular cushion 4 (FIG. 11). In case protective liners 5 with a minimalwall thickness are employed, the heat-resistant reinforcing material incombination with annular cushion 4 protects reliably the thin wall ofliner 5 from burn-through in the course of welding. The impact of vacuumupon the wall of protective liner 5 during the sealing-off of theannular cavity averts the loss of stability of the shape of thin-wallliner 5. When using liners 5 with a wall thickness within the lowerrange of values, the use of excessive pressure to act upon liquidsealant material 10 is inadmissible in the process of sealing-off of thewelded-joint annular cavity.

The proposed method is implemented as follows.

In the initial state, thin-wall liner 5 (FIG. 7) has the form of acylinder with outer diameter D_(y0) and wall thickness S. This being thecase, the outer diameter of protective liner 5 does not exceed theminimally allowable internal diameter of pipes 1 to be joined (takinginto account the maximal permissible departures of their geometricparameters). Then, perimeters of annular holes at ends of both pipes 1to be joined (internal diameters) are measured. When doing so, maximallyaccurate account of actual internal geometric parameters of pipes 1(internal diameter and out-of-roundness of the pipes) is provided.Further, both parts of the thin-wall liner are expanded by means ofplastic deformation (FIG. 8). In the process of such deformation, at theends of liner 5, on their outer surface, annular projections(reinforcement ribs) can be formed. One part of liner 5 is expanded todiameter D_(y1). In such a case, the diameter D_(y1) is derived from theperimeter of the first pipe 1 to be joined, taking into account therequired mounting gap between liner 5 and the inside surface of pipe 1and the thickness of inside protective coating 3 of the pipes. Theminimum mounting gap shall be no less than 0.1 mm per side. It is due tothe minimally allowable thickness of the adhesive layer (sealant layer).When determining the mounting gap, the following is also taken intoconsideration: condition of the inside surface of the pipes to beconnected (curvature of the inside surface and availability offactory-made longitudinal weld joints); availability and thickness ofthe annular cushion; availability and thickness of the reinforcingmaterial; penetrability and viscosity of the sealant agent employed.

The other part of liner 5 is expanded to diameter D_(ye) derived fromthe perimeter of the actual opening in second pipe 1 taking into accountthe mounting gap and the thickness of inside protective coating 3 of thepipes. Such shaping of thin-wall liner 5 parts ensures matching of liner5 ends to actual interior dimensions of pipes 1 (to be joined) withminimal annular gaps between the outer surface of liner 5 and the insidesurface of pipe 1. In the case of any out-of-roundness/ellipticity ofthe pipes in question prior to the assembling, thin-wall protectiveliner 5 is deformed to a shape matching that of both pipe ends to bejoined. Owing to good flexibility and resilience of the thin-wallprotective liner, the operation of plastic deformation of the liner isan easily feasible one.

One part of protective liner 5 so prepared is introduced into fixed pipe1 until it gets rested against sealant 4 applied onto the inside surfaceof pipe 1. Second pipe 1 is pushed onto the other part of protectiveliner 5 until it gets rested against sealant 4 applied inside the pipe.Ends of liner 5 are sealed off. After that, the joint of pipes 1 iswelded.

When injecting the sealant material via vacuum reservoir 11 (see FIGS. 1and 2), vacuum reservoir 11 is connected to process hole 8 of weldedjoint 2. More than one hole 8 made in either one pipe 1 or both of themcan be used. Vacuum reservoir 11 is connected, through stop valves 16,with vacuum pump 13 and tank 12 with the sealant material. Additionally,vacuum gauge 18 and vacuum break valve 14 are connected to vacuumreservoir 11. For visual inspection purposes, vacuum reservoir 11 has asight hole. Vacuum reservoir 11 is placed above the highest point ofweld joint 2 to be insulated. Via process hole 8, vacuum in annular gapsand cavities is achieved by means of vacuum pump 13. For some time,valve 16 that connects vacuum reservoir 11 to vacuum pump 13 is closed.With the help of vacuum gauge 18, the rate of gas/air inflow intoevacuated weld joint 2 is measured. Airtightness of preliminaryinsulation of weld joint 2 is checked. Upon completion of suchairtightness check, evacuation is resumed. Then, with vacuum pump 13turned on, valve 17 connecting vacuum reservoir 11 to tank 12 withsealant material 10 is opened. Under the effect of vacuum, sealantmaterial 10 is fed to vacuum reservoir 11. Once vacuum reservoir 11 isfilled with sealant material 10 to a preset level, valve 17 for feedingthe sealant material is closed. When doing so, no air inflow to thevacuum reservoir via valve 17 is allowed. Under gravity and thecapillary effect, sealant material 10 fills the pre-evacuated cavitiesand gaps around weld joint 2 being insulated. The level of liquidsealant material 10 in vacuum reservoir 11 gradually lowers. Once thelevel of sealant material 10 in vacuum reservoir stops changing, thepumping is turned off and vacuum is broken. As a result, atmosphericpressure starts acting upon the liquid material and thereby sealantmaterial 10 is squeezed into microscopic gaps of the annular cavity ofthe weld joint being insulated. In exceptional circumstances, forinstance, in the case of defective preliminary insulation of the annulargaps along liner 5 butts, compressed air is charged, via valve 15, tovacuum reservoir 11 after vacuum is broken. It allows to ensurepenetration of sealant material 10 into the minutest gaps, micro-cracksetc. At the final stage, outgoing inspection of the airtightness of weldjoint 2 insulation is performed by means of evacuation, shutoff of theline connecting to vacuum pump 13, and assessment of the rate of gas/airinflow into vacuum reservoir 11. Once the checking is completed, processhole 8 is sealed off.

When using the vacuum infusion method for injection of sealant material10 (see FIGS. 3 and 4), at least two process holes are made in the zoneof weld joint 2—one hole 8 above pipe 1 and second hole 19 in the bottompart of pipe 1. Vacuum reservoir 11 is connected to upper process hole 8of the weld joint. Tank 12 with sealant material 10 is connected, bymeans of a hose and shutoff valve 17, to lower process hole 19.

Through upper process hole 8, vacuum is achieved in annular gaps andcavity of the joint with the help of vacuum pump 13. For some time,valve 16 that connects vacuum reservoir 11 to vacuum pump 13 is closed.With the help of vacuum gauge 18, the rate of gas/air inflow intoevacuated weld joint 2 is measured. Airtightness of prior insulation ofweld joint 2 is determined. Upon completion of such airtightness check,evacuation is resumed. Then, with vacuum pump 13 turned on, lower valve17 connecting lower process hole 19 of the weld joint with lower tank 12with sealant material 10 is opened. Under the effect of vacuum, sealantmaterial 10 from lower tank 12 is fed to the annular cavity and gaps.Under gravity, at first the lower part of the cavity and gaps is filled.Upon impregnation/filling of the entire volume of cavity and gaps in theevacuated weld joint by the sealant material, the fluid starts fillingupper vacuum reservoir 11. At this moment, lower valve 17 for deliveryof the liquid sealant material is closed. The valve connecting uppervacuum reservoir 11 to vacuum pump 13 is closed. Airtightness ofinsulation is checked through measuring the rate of gas/air inflow.Vacuum is broken in upper vacuum reservoir 11. Atmospheric pressureexerts influence upon liquid sealant material 10 in the upper vacuumreservoir, thereby ensuring the filling of micro-cracks and otherdefects in the cavity and gaps of the welded joint to be insulated. Ifnecessary, excessive pressure is created in upper vacuum reservoir 11,which ensures penetration of liquid sealant material into micro-cracksand discontinuity flaws (according to results of some studies, undervacuum impregnation conditions, liquid sealant material 10 penetratesinto micro-cracks less than 50 to 70 nm). Process holes 8 and 19 aresealed off. After the vacuum infusion, practically no voids ornon-impregnated areas in the space between liner 5 and inside surface 7of the pipeline's weld joint being insulated are left. Liquid sealantmaterial 10 polymerizes. As a result, an airtight monolithic joint ofouter surface 6 of liner 5 with inside surface 7 of the pipeline jointbeing insulated is formed, which averts penetration of the medium (to betransported via the pipeline) to within the weld joint area.

In another embodiment of the method, reinforcing material, wellimpregnable and resistant to corrosive environments, e.g. glass fabric,is placed onto the central area of liner 5 between said annularprojections 9. After polymerization of liquid sealant material 10 thatimpregnated the reinforcing material, the so-formed reinforcedmonolithic block is converted into a very firm joint. In accordance withthis embodiment, liner 5 can be made of either stainless steel orordinary carbon steel practically without any loss in reliability ofwelded-joint insulation since polymerized impregnating material 10reinforced with strong material resistant to corrosive environments iscapable of ensuring a high-quality insulation of the welded joint evenafter penetration corrosion of steel liner 5. Also, such liner 5 can bemade of thin-wall (0.1 to 2.0 mm) steel as its flexure under vacuumconditions does not exercise critical effect on the condition of thegaps and the final quality of welded-joint insulation. All the aboveallows ensuring economic insulation of such welded joints without anyharm to reliability of inside insulation of the welded joint.

When sealing the annular gaps along liner 5 butts, the reinforcingmaterial prevents the thixotropic sealant from penetration into theinner annular cavity between pipes 1 and liner 5, thereby securing theoptimal conditions for preliminary sealing. In the process ofimpregnation, liquid sealant material 10, exposed to vacuum conditions,penetrates without any serious barriers, through the reinforcingmaterial to impregnate the entire annular cavity of the joint beinginsulated. After polymerization of the liquid sealant, the producedreinforced monolithic block grows into a very firm joint. In the courseof evacuation, the reinforcing material prevents the liner wall fromflexure, as well as the weld joint cavity from collapse. It ensures auniform gap of the cavity to be sealed off.

Also, the proposed method can be implemented using annular cushion 20.In FIGS. 9 and 10, annular cushions are presented with point-likeprojections (FIG. 9) or intermittent reinforcement ribs (FIG. 10) on theinside surface of the cushion. Annular cushion 20 is positioned at thecenter of protective liner 5 (FIG. 11), on its outer surface. After themounting, the outer surface of annular cushion 20 abuts on the surfaceof pipes 1 to be joined and covers the gap between them. In the processof welding of the joint root, annular cushion 4 averts uncontrolledoutflow of liquid metal from the molten pool, thereby preventingthin-wall protective liner 5 from a burn-through by molten metal orwelding arc. Projections 21 on the inside surface of annular cushion 20rest against the outer surface of protective liner 5. The area ofcontact between annular cushion 20 and protective liner 20 is severaltimes lower than the inside surface of annular cushion 20. As a result,the thermal flux from annular cushion 20 to protective liner 5 alsodeclines by several times. Additionally, local projections 21 on annularcushion 20 provide a guaranteed gap 22 between annular cushion 20 andprotective liner 5, which allows liquid sealant material 10 to fillwithout obstruction all cavities and gaps of the weld joint beinginsulated.

As the sealant material, two-component adhesives can be employed, e.g.epoxy or polyurethane resins. Polymerization of such resins takes aperiod of time depending on the temperature. Therefore, when performingthe sealing of welded joints in winter, one may have to provide localheating of insulated joints to ˜10-20° C. To accelerate thepolymerization process, the warm-up temperature can be increased inaccordance with the specifications for the sealant in use. Oncepolymerization of the liquid sealant compound is complete, a sealed-offmonolithic assembly is formed, which precludes any penetration ofcorrosive media being transported via the pipeline to the ferrous metalof the joint. Monolithic insulation of a weld joint in conformity withthe method proposed is efficient practically at any permissible pipelinepressures, up to 200 MPa.

Below, a specific embodiment of the proposed method is provided.

Pipes 1 to be joined have the nominal outer diameter of 219 mm, internaldiameter of 207 mm, and wall thickness of 6 mm.

Inside protective coating 3 is of epoxy type, the indent of coating 3from the pipe 1 edge is 50 mm (the thickness of coating in thenon-protected part of the pipe is 300 μm).

In its initial condition, stainless steel liner 5 had the shape of aregular cylinder with two alignment petals welded in the center of liner5 with short weld joints. The outer diameter of the protective liner was198 mm, wall thickness was 1.00 mm. The liner width was 200 mm.

Vacuum was created with the help of rotary vane pre-evacuation pump 13(Busch R5).

Vacuum was measured by with the help of a Testo 552 vacuum gauge.

The preliminary operations were performed as follows. Actual innerperimeters of pipe ends of pipes 1 to be joined were measured. For thispurpose, a steel cone made of thin sheet steel 0.5 mm was used. The conehad a scale, namely, circular lines on the outer surface. These circularlines are gauged. On the basis of perimeters of both pipes 1 to bejoined, the actual nominal inner diameter was determined with adjustmentfor ellipticity of pipes 1. The first pipe 1 had the outer diameterequal to 214 mm, the inner one, 202 mm, and the wall thickness, 6 mm.The second pipe 1 had the outer diameter equal to 217 mm, and the innerone, 205 mm. The actual nominal diameter of pipes 1 to be joined wascalculated taking the protective coating thickness into account. Thefirst pipe had the inner diameter (with the coating) equal to 201.4 mm.For the second pipe, this value was 204.4 mm. Their actual innerdiameters were written down with a chalk on the outer surface of thepipes. The mounting gap was taken equal to 0.4 mm. The maximal outerdiameters of protective liner 5 ends were determined with reference toannular projections 9—201 and 204 mm respectively. On a W6 retrofittedmobile hydraulic expansion machine (Hornung company, Germany), both endparts of pipes 1 were shaped in field conditions. The total time ofshaping of both ends of protective liner 5 (with adjustment for settingrequired geometric parameters) was 30 sec. The accuracy of the shapingwas 0.1 mm. At both ends of liner 5, on its outer surface, the maximaldiameters determined by annular projections 9 (201 and 204 mmrespectively) were written down with a chalk.

Welded joint 2 (FIG. 1) of steel pipes 1 with inside protective coating3 was sealed off as follows in accordance with the method proposedherein.

In the upper part of the fixed pipe, at a distance of 20 mm from itsend, process hole 8 with a diameter of 5 mm was made. Hole 8 wasthreaded (M6). An adapter for connection of a hose was mounted on tacksto hole 8 at the outer surface of pipe 1. The hole of the adapter wasclosed with a steel plug. Inside surfaces of pipes 1 to be joined wereblown with compressed air and wiped clean with a rag. The depth oftreatment of both ends reached 120 mm. Then, with the help of a metalbrush, products of corrosion were removed from the inside surface areasbeing treated. Inside surfaces of pipe 1 were blown once again. Ontoinside coating 3 of end parts of pipes 1 (at a distance of 85 mm fromboth parts of the ends being joined), thixotropic sealant material (LEOQUARTZ metal-filled polymer) was applied in the form of continuousannulus 4 along the whole perimeter of pipe 1. Liner 5 with two annularprojections 9 at its ends was placed coaxially inside fixed pipe 1 withan actual inner diameter of 201.4 mm. This being the case, some part ofprotective liner 5 with the maximal diameter of 201 mm was pushed intofirst pipe 1. Liner 5 was gently pushed in the pipe to two petals(stops) welded there. Annular projection 9 at the edge of liner 5replaced thixotropic sealant 4 in pipe 1 along the movement of liner 5and sealed off the first edge of liner 5. The stopping petals of liner 5were welded (optionally, they can be soldered) to the butt of pipe 1.Then, with the help of lifting gear, second pipe 1 was mounted. Whendoing so, second pipe 1 was pushed smoothly until the contact to liner 5stops. The second edge of liner 5 was sealed off by sealant annulus 4inside second pipe 1. The gap between inside surfaces of pipes 1 beingjoined and the adjusted outer surface of both parts of liner 5 was 1.5mm per side. After that, the joint of pipes 1 was welded (manual arcwelding). Once the metal cooled down, the connection between the processhole adapter and the pipe was sealed off with thixotropic sealant. 24hours later, the weld joint was sealed off using the vacuum impregnationmethod in accordance with the diagram displayed in FIG. 1. Vacuumreservoir 11 of the impregnation machine was connected to the adapterwith the help of a vacuum hose. Liquid sealant (viz.,RAKU-TOOLEL-2203/EH-2970-1 resin) in the amount of 500 ml was prepared(mixed). The so-prepared resin was poured into reservoir 12 for thesealant material mounted on the impregnation machine. Busch R5 vacuumpump 13 was turned on. The cavity around weld joint 2 was evacuated byopening valve 16 (FIG. 1). Within 30 sec, the absolute pressure atvacuum gauge 18 reached 1.0 mbar. In two minutes, valve 16 was closedand the airtightness of the weld joint was checked. The pressure in theweld joint being insulated was monitored. Readings of gauge 18 did notchange for five minutes. The preliminary sealing-off of the joint wasperformed with a good quality. Valve 16 was opened and weld joint 2 wasevacuated to a deeper vacuum. In a minute, the resin was fed to vacuumreservoir 11 by means of opening valve 17. Vacuum reservoir 11 wasfilled with the resin in the amount of ˜300 ml. The line for delivery ofresin to vacuum reservoir was shut off. Visual monitoring of the resinlevel was performed via the viewport in vacuum reservoir 11. The levelof resin in reservoir 11 came to a stable state within two minutes. In aminute after the level of resin in vacuum reservoir 11 became stable,evacuation valve 16 was closed. Vacuum in reservoir 11 was broken by ashort-time opening of valve 14. Compressed air with an overpressure of 1bar is supplied to vacuum reservoir 11. Two minutes later, the supply ofcompressed air was closed and the system was evacuated to 1.0 mbar. Theevacuation line was shut off by valve 16. The airtightness of the weldjoint was checked. Readings of the vacuum gauge did not change for 5minutes. The joint was sealed off reliably. Vacuum in reservoir 11 wasbroken and the equipment was turned off. At process hole 8, the tacks onthe adapter were removed with the help of a hammer and a chisel, afterwhich the adapter was removed. Process hole 8 was sealed off with resinand a steel screw (M6). Polymerization of sealant material 10 wasachieved through natural solidification.

The group of inventions claimed herein streamlines the technology forinsulation of welded joints of pipelines, which reduces the impact ofhuman factor upon the quality of weld joint insulation, enhancesessentially the reliability and service life of such insulation, reducesthe material consumption of associated operations, diminishes the effectof inner geometry violations, in particular, out-of-roundness of pipes,upon the quality and laboriousness of pipeline weld joint insulation,reduces the hydraulic resistance of the pipeline owing to enhanced flowarea of insulated weld joints, allows the use of an easy and reliablemethod for controlling the airtightness of pipeline weld jointinsulation, allows inside insulation of hard-to-reach weld joints,curtails the pipeline construction time due to eliminated impact of theprogress of work associated with weld joint insulation upon thepossibility to assemble and weld further pipes and strings, eliminatesthe negative effect of burrs and icicles that appear in the course ofwelding upon the quality of pipeline weld joints, allows insulating weldjoints of pipelines with arbitrary inside protective coating andarbitrary diameter.

1-8. (canceled)
 9. Method for inside anti-corrosion protection of weldedjoints of pipes with an interior protective coating, which comprises:placement of a protective liner coaxially inside the pipes to be joined,with formation of an annular cavity between the outer surface of theliner and the inside surface (to be insulated) of the weld joint of thepipes with adjacent coating-protected areas; welding of the pipe ends;sealing-off of the annular cavity at liner edges; filling of the annularcavity with a liquid sealant agent via at least one process hole in oneor both pipes with subsequent polymerization of the agent, wherein priorto the placement of the protective liner, it is plastically deformed bymeans of stretching the liner parts to ensure matching the shape andinternal diameter of each part of the liner to the shape and internaldiameter of the opening of respective pipe in the area of the joint,taking into account the mounting gap between them and the thickness ofthe inside protective coating, and the placement of the protective lineris effected in the form of inserting one part of the liner into one pipeuntil it gets rested against the sealant applied onto its insidesurface, and then pushing the second pipe onto the other part of theprotective liner until it gets rested against the sealant on the insidesurface of the second pipe.
 10. Method according to claim 9, wherein theannular cavity is filled with a liquid sealing material by means ofevacuating the annular cavity followed by feeding said material therein,and then exposing said material to the effect of atmospheric or excesspressure.
 11. Method according to claim 9, wherein when placing theprotective liner, in between the protective liner and the weld joint asteel annular cushion is arranged, which contacts with its outer surfaceto the weld joint surface and has projections on its inside surface thatare in contact with the outer surface of the protective liner, and whenwelding pipe ends, they are welded to the steel annular cushion. 12.Method according to claim 9, wherein the protective liner has annularprojections on the outer surface of its end parts.
 13. Method accordingto claim 9, wherein in the course of the plastic deformation of theliner annular projections on the outer surface of its end parts areformed.
 14. Method according to claim 12, wherein, prior to theplacement of the protective liner, a reinforcing, well impregnablematerial resistant to aggressive environments is applied onto theliner's outer surface in between the annular projections.
 15. Methodaccording to claim 9, wherein the airtightness of weld joint insulationis checked both prior to and after the filling of the annular cavitywith the liquid sealant material by means of evacuation and subsequentassessment of the rate of air/gas leakage into the annular cavity. 16.Method according to claim 9, wherein the protective liner is made ofstainless steel and has a wall thickness ranging from 0.1 to 6.0 mm.